I found out that Dr Web Plesk uses a significant amount of memory. If I am not mistaken this is an antivirus for mail, isn't it ? Well as I am not using email services on my server how can I disable this ? I have attached to this post all services I have and don't see that one.
Dr.web (called Plesk Premium Anti-virus) can be uninstalled via Tools & Settings > Updates. Which opens a new tab/window on which you can click the "Add/Remove Components" and de-select the Premium antivirus for servers option.